Alfred Johan Harstad was born July 30, 1886 in Grove City, Minnesota, the son of Norwegian immigrant parents. He was one of Montana's most colorful figures in mineralogical circles. He served in World War I with the celebrated 163rd Montana Infantry Regiment, and upon returning he settled in the small town of Wolf Creek, north of Helena, where he opened The Gem Shop in 1919. Ads for The Gem Shop never identified the owner by name. He listed his occupation on the 1920 census as "house carpenter," indicating that the minerals must have been a sideline, though a very serious one. During the early years of Rocks & Minerals he ran a column called The Sluice Box, under the pen name of “A. Rifle.” But he also wrote a number of articles for the magazine under his own name, including “The Montana Agate” (November 1938). He married Julia Catherine Hyatt in March 1924, five years after the establishment of The Gem Shop. They had one son, John Lee Harstad (born 1929 in Helena) and one daughter, Mary Ann Harstad (born 1933 in Helena).

Harstad continued to operate his shop in Wolf Creek until December 1931, when he finally considered himself prosperous enough to move to the big city of Helena, setting up shop at 16A Kohrs Block. He purchased the large mineral stock of the Brooklyn dealer Frederick Braun (q.v.) in 1933. The Gem Shop, despite its name and its lapidary stock, was dedicated primarily to the serious mineral collector and did a substantial mail order business. He claimed to have over 90% of the mineral species listed in George English's Getting Acquainted with Minerals, He ran half-page to full-page ads for many years, but went down to a small ad saying only "Choice Minerals for the Collector, catalog 10c" in November 1941. His last ad as The Gem Shop appeared in the May 1943 issue of Rocks & Minerals, but he returned a few months later in the November 1944 through February 1945 issues advertising as "A. J. Harstad" and using the same post office box number. He offered a new “streamlined” method of buying specimens based on the honor system – no advance payment was necessary. He would send you the minerals you asked for and you would send him a check for the ones you kept and would return the rest.

Harstad died on September 5, 1946, in a one-car accident when he suffered a heart attack while driving and his vehicle left the road east of Bonners Ferry, Idaho, plunged down a 400-foot embankment and landed in the Moyle River. He was described in his obituary as "a genial friend and a pleasant and wholesome companion in the field when collecting." His wife Julia continued the business for a short time but siffered a breakdown and had to sell the shop (buyers unknown); the shop remained open at least through 1948. His mineralogy books were eventually donated by the family to the Colorado School of Mines.